The New Mighty Mouse: The Magic Mouse From Apple
crunchgear.com
crunchgear.com
I'm going to test it out at the store tonight.
They will have the new iMacs on display tomorrow, so I'll be able to really try it then.
Also, back in the old linux days when most PCs only had 2 mouse buttons, people could click with both buttons to emulate the middle button. This was a standard option in the xfree86.config file. I would imagine something like this would be possible if the mouse can detect 5 independent touches on the pad.